1. Field of the Invention
The present invention relates to a fuel cell system which can recover pressure energy of an exhaust gas by expanding the exhaust gas in a regenerator after oxygen has been consumed in a fuel cell and using the recovery energy to assist the power driving the compressor.
2. Description of the Related Art
Japanese Unexamined Patent Publication (Kokai) No. 7-14599 discloses a fuel cell system. FIG. 6 in the attached drawings shows such a prior art, wherein air sucked through an air feeding conduit 60 is supplied to a fuel cell 63 after being pressurized to a certain pressure by a compressor 62 driven by an electric motor 61. Oxygen is consumed, from the supplied air, in the fuel cell, and an exhaust gas is discharged from the system to the atmosphere after being expanded in an expander 65 coupled to the compressor 62 and the motor 61 with a common shaft 64.
The produced water contained in the exhaust gas is separated by liquid separators 67 and 68 provided in an air discharging conduit 66, and is collected into an open type reservoir 69, from which the stored water is fed to a jet nozzle 71 by a pump 70 and injected into the air feeding conduct 60 for the purpose of humidifying the process air.
That is, as stated above, it is very efficient for the produced water contained in the exhaust gas in the fuel cell 63 to be separated and collected, for the purpose of humidifying the process air. Such water is usable not only for maintaining the proton conductivity of a cation exchange membrane in the fuel cell 63 but also for cooling and lubricating the compressor 62. In this respect, a scroll type compressor particularly could benefit from the use of such water, and there have been many proposals for improving the scroll type compressors or expanders.
However, when the residual (pressure) energy remaining in the exhaust gas from the fuel cell is converted to mechanical energy by the regenerator (expander) and fed to the compressor via the common shaft, a difference is generated between the pressure of the discharge air from the compressor and the pressure of the exhaust gas introduced into the regenerator due to a pressure loss in the fuel cell, whereby the exhaust gas is sometimes made to expand in the regenerator to a subatmospheric pressure, resulting in undesirable energy consumption.
An object of the present invention is to solve the above-mentioned problems in the prior art while maintaining merits of a scroll type compressor and a scroll type regenerator, by recovering the residual energy from the exhaust gas of a fuel cell to achieve an efficient power assist for the compressor without useless power consumption.
A fuel cell system, according to the present invention, for solving the above problems, comprises: a fuel cell having an air feeding passage and a gas exhaust passage; a scroll type compressor arranged in the air feeding passage, said compressor including a stationary scroll and a movable scroll; a scroll type regenerator arranged in the gas exhaust passage, said regenerator including a stationary scroll and a movable scroll; a motor having an output shaft having opposite ends; the movable scroll of the compressor being operatively coupled to one end of the output shaft of the motor, the movable scroll of the regenerator being operatively coupled to the other end of the output shaft of the motor symmetrically with the movable scroll of the compressor; and the pressure ratio of the regenerator being smaller than that of the compressor by an amount corresponding to the pressure loss of the gas across the fuel cell.
Since the compressor and the regenerator, both of which are of a scroll type, are coupled to the opposite ends of the motor output shaft, it is possible to realize an extremely simple air feeding mechanism which is particularly suitable for a vehicle fuel cell system. Also, since the pressure ratio of the regenerator is selected to a value capable of sufficiently compensating for a pressure loss of supplied air occurring in the fuel cell, it is possible to prevent a phenomenon from occurring in that exhaust gas introduced into the regenerator excessively expands to a subatmospheric pressure; in other words, the transmission of negative torque due to the rotation of the regenerator to the motor output shaft is completely avoidable to facilitate the effective power assist for the compressor.
If the fuel cell system is adapted so that the water separated from the exhaust gas is pumped to the water introduction device of the scroll type compressor, it is possible not only to humidify the supplied air but also to suitably cool and lubricate the compressor itself. Also, if both the compressor and the regenerator are arranged so that the peak variation of the torque of the compressor is generally in phase with the peak variation of the torque of the regenerator, the power transmission between the compressor and the regenerator is further enhanced. Moreover, if the number of scrolling walls formed in the movable scrolls of the compressor and the regenerator is adjustable, it is possible to easily select a suitable relative pressure ratio between the compressor and the regenerator in correspondence with the pressure loss within the fuel cell.